1. Field of the Invention
The present invention relates to a motor drive control apparatus and method having a motor current limit function, which can be applied to a motor driven throttle valve control in an internal combustion engine.
2. Related Art
In a motor driven throttle control apparatus for vehicles, a direct current motor is coupled to a throttle valve of an internal combustion engine. The motor is driven with an electric current (motor current) of 100% duty at the time of starting the motor drive from one position to another to improve responsiveness of the throttle valve. The motor current is reversed temporarily to brake the motor so that the throttle valve is stopped at a target throttle position or angle, when the throttle valve rotates to a position near the target throttle position. The current increases excessively when the motor locks due to jamming of foreign obstacles with the throttle valve. The current is shut off to protect semiconductor switching devices, when the motor lock is detected based on the condition that the throttle valve does not rotate to the target position within a predetermined time period.
The motor tends to lock slightly when water on the throttle valve freezes. However, the motor will rotate again normally when the supply of the motor current is continued, unless the degree of freezing is substantial. If the time period for the motor lock detection is set short, the current is shut off unnecessarily even when the motor lock is nominal, such as when the degree of freezing is not substantial. If the time period for the motor lock detection is set long, semiconductor switching devices of large size and cost are required.
In U.S. Pat. No. 5,712,550, a motor current is limited to below a predetermined level to reduce the power capacity and cost of semiconductor switching devices. However, the motor drive with the limited motor current will result in insufficiency of the drive torque for starting the motor drive from one rotation position to another and the braking force for braking the motor, thereby lessening the responsiveness of the throttle valve.